Stabilizing a gas turbine engine via incremental tuning during transients

ABSTRACT

Methods and systems are provided for automatically tuning a combustor of a gas turbine engine during a transient period, such as when a state of the gas turbine engine is changing. Once it has been determined whether the state of the gas turbine engine is changing, it is then determined whether a lean blowout is imminent, which is based conditions being monitored. A stability bias is applied to the system if either the state is changing or if lean blowout is imminent until the lean blowout is no longer determined to be imminent. The stability bias monitors operating conditions of the gas turbine engine and determines when one of the operating conditions has overcome a threshold value. Once a threshold value is overcome, a fuel flow fraction is adjusted by a predefined increment. The application of the stability bias is gradually terminated once it is determined that the lean blowout is no longer imminent.

CROSS REFERENCE TO RELATED APPLICATIONS

This Nonprovisional Patent Application is a continuation-in-part of U.S.patent application Ser. No. 12/786,189, filed May 24, 2010, entitled“STABILIZING A GAS TURBINE ENGINE VIA INCREMENTAL TUNING,” which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention generally relates to automatically tuning a gasturbine engine. More specifically, a process and system are identifiedfor providing a control system to automatically tune the gas turbineengine during transients by incrementally adjusting one or more fuelflow fractions within a combustor or incrementally adjusting the gaseousfuel temperature.

BACKGROUND OF THE INVENTION

Gas turbine engines operate to produce mechanical work or thrust.Specifically, land-based gas turbine engines typically have a generatorcoupled thereto for the purposes of generating electricity. The shaft ofthe gas turbine engine is coupled to the generator. Mechanical energy ofthe shaft is used to drive a generator to supply electricity to at leasta power grid. The generator is in communication with one or moreelements of a power grid through a main breaker. When the main breakeris closed, electrical current can flow from the generator to the powergrid when there is a demand for the electricity. The drawing ofelectrical current from the generator causes a load to be applied to thegas turbine. This load is essentially a resistance applied to thegenerator that the gas turbine must overcome to maintain an electricaloutput of the generator.

Increasingly, a control system is used to regulate the operation of thegas turbine engine. In operation, the control system receives aplurality of indications that communicate the current operatingconditions of the gas turbine engine including pressures, temperatures,fuel flow rates, and engine frequencies. In response, the control systemmakes adjustments to the inputs of the gas turbine engine, therebychanging performance of the gas turbine engine based on the plurality ofindications in light of look-up tables coded into the memory of thecontrol system. Over time, this performance may fall outside a preferredoperating range due to mechanical degradation of the gas turbine engineor changes in operational conditions such as ambient temperature or fuelconstituents. For instance, the gas turbine engine may start operatingbeyond regulated emissions limits. As such, multiple manual tunings arerequired to update the control system. Manual-tuning is labor intensiveand can create business-related inefficiencies, such as extendeddown-time of the gas turbine engine and operator error in the course oftuning. In addition, because there are specific windows of time wheremanual tuning may not be available (e.g., high dynamics events), butwhere performing a tuning operation would be beneficial to protectagainst potential damage to hardware, automatically tuning during thosewindow will capture those benefits typically missed with manual tuning.

SUMMARY

In accordance with the present invention, there is provided a novel wayof monitoring operating conditions of a gas turbine engine andresponding to conditions which exceed predetermined upper limits.Initially, various engine operating conditions can be monitored. By wayof example, these operating conditions may include, but are not limitedto, emissions, and combustor dynamics modes, such as Lean Blowout (LBO),Cold Tone (CT), Hot Tone (HT), and Screech. When a monitored operatingcondition exceeds one or more of the predetermined upper limits, anengine parameter is changed to adjust this condition to bring it withinthe limits, thereby tuning the gas turbine engine.

More specifically, pressure fluctuations, also called combustiondynamics, may be detected (e.g., utilizing pressure transducers) in eachcombustor of the gas turbine engine. Next, a Fourier Transform may beapplied to the pressure signals to convert the pressure signals into anamplitude versus frequency format. The maximum amplitude atpre-determined frequency band, within a timeframe, may be comparedagainst a pre-determined upper pressure limit, or alarm level limit.Incident to comparison, when it is ascertained that the upper pressurelimit is exceeded by the maximum amplitude, an appropriate correctiveaction is taken. In some instances, the appropriate action is carriedout manually. In another instance, the appropriate action is implementedby the control system. For instance, the control system may initiate aprocess of altering one or more fuel flow fractions within a fuelcircuit of the combustor. In an exemplary embodiment, one fuel flowfraction is altered at a time by a predefined increment. As describedherein, the phrase “predefined increment” is not meant to be construedas limiting, but may encompass a wide range of adjustments to the fuelflow fractions. In one instance, the predefined increment is a uniformamount of adjustment that is consistently applied to one or more of thefuel flow fractions. In another instance, the predefined amount is avaried amount of adjustment that is altered across fuel flow fractionsor across individual adjustments to a particular fuel flow fraction. Byaltering the fuel flow fractions in this manner, the fuel-air mixingwithin the combustor is changed, thus, affecting the combustionsignature. Upon affecting the combustion signature, the pressurefluctuations are altered.

This altered combustion dynamics amplitude, once stabilized, is againcompared against the predetermined upper limit to verify whether theadjusted fuel flow fraction has moved the amplitude within an acceptablerange. If the amplitude remains over the predetermined upper limit, thefuel flow fraction is once again adjusted by the predefined incrementand the process is recursively repeated as necessary. Advantageously,changes are made to the fuel flow fraction consistently and uniformly atthe same predetermined increment, thereby saving processing time tocompute a customized value of an increment each time the predeterminedupper limit is exceeded.

Accordingly, in an exemplary embodiment of the process of auto-tuning, acontrol system for monitoring and controlling the gas turbine engine isprovided. This control system generally manages a majority of theprocesses involves with auto-tuning the combustor, and may be referredto as an auto-tune controller. Initially, the process includesmonitoring the combustion dynamics and emissions of the combustor for aplurality of conditions. Upon determination that one or more of theconditions exceed the predetermined upper limit, a fuel flow fraction toa fuel circuit is adjusted by the predetermined amount. The controlsystem, or auto-tune controller, continues to monitor the combustiondynamics and to dynamically adjust the fuel flow fraction by thepredetermined amount until the combustion dynamics fall below thepredetermined upper limit.

Further, in an alternate embodiment of the process of auto-tuning, thegas turbine engine is monitored and, based on the data recovered frommonitoring, automatically adjusted. Generally, the automatic adjustmentinvolves incrementing upward or downward the fuel flow fraction in orderto maintain combustion dynamics and emissions within a preferredoperating range, or above/below a limit. In particular, the alternateprocess initially includes detecting pressure signals in the combustorduring the step of monitoring. Subsequent to, or coincident with, thestep of monitoring, an algorithm is applied to the detected pressuresignals. In one instance, applying the algorithm involves performing aFourier Transform on the pressure signals to convert the pressuresignals into frequency-based data or a spectrum. The amplitude of thefrequency-based data is compared to predetermined upper limits(amplitude) for different known conditions. If it is determined that theamplitude of the frequency based data exceeds its respectivepredetermined upper limit, an incremental adjustment in the fuel flowfraction is made. In one instance, the incremental adjustment is achange in the fuel flow fraction carried out in a fixed andpre-determined amount. This incremental adjustment can either increaseor decrease the fuel flow fraction depending on the frequency band beinginspected and/or the type of fuel circuit being adjusted. This alternateprocess recursively repeats until the frequency-based data indicates thegas turbine engine is operating within a suggested range.

In one instance, if the alternate process has been recursively repeateda number of times such that the fuel flow fraction for a specific fuelcircuit has reached a maximum allowable value, a second fuel flowfraction that affects a second fuel circuit may be adjusted by apredefined fixed amount. If the frequency-based data measured indicatethat gas turbine engine is operating within a suggested range, then thealternate process is concluded. Otherwise, the second fuel flow fractionis recursively adjusted by the same predefined fixed amount until eitherthe amplitude of the frequency-based data moves to acceptable levels ora maximum allowable value of the second fuel flow fraction is reached.In embodiments, the predefined fixed amount may vary based on which fuelflow fraction is being monitored, the number of increments of adjustmentthat have been applied to a particular fuel flow fraction, or anotherother conditions or parameters that impact the adjustment of the fuelflow fraction.

In another instance, if the alternate process has been recursivelyrepeated a number of times such that the fuel flow fraction for aspecific fuel circuit has reached a maximum allowable value, theincremental adjustment of the fuel flow fraction is ceased. Uponcessation of the incremental adjustment, an adjustment of gastemperature may be invoked to bring the operation of the gas turbineengine within a particular performance range. If the adjustment to thegas temperature fails to properly tune the gas turbine engine, an alarmindication is communicated to an operator. This alarm indication may becommunicated to a console, a pager, a mobile device, or anothertechnology adapted to receive an electronic message and relay anotification to the operator. The operator will be given the option ofincrementing the fuel gas temperature or incrementing the engine firingtemperature. If this option is selected, the auto-tune controller willincrementally adjust either of these parameters and repeat this processuntil the unit is in compliance or a maximum limit is reached. In theevent this process is not successful, an alarm indication may alert theoperator that automatic tuning has failed to bring the operation of thegas turbine engine within the suggest range, and that manual adjustmentsto the combustor or the control system are recommended prior tocompleting tuning.

Additional advantages and features of the present invention will be setforth in part in a description which follows, and in part will becomeapparent to those skilled in the art upon examination of the following,or may be learned from practice of the invention. The instant inventionwill now be described with particular reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in detail below with reference to theattached drawing figures, wherein:

FIG. 1 is a block diagram of an exemplary tuning environment suitablefor use in embodiments of the present invention;

FIG. 2 is an exemplary chart depicting recommended fuel flow fractionadjustments for a fuel-rich condition, in accordance with an embodimentof the present invention;

FIG. 3 is an exemplary chart depicting recommended fuel flow fractionadjustments for a combustor that is provided with two injection ports,in accordance with an embodiment of the present invention;

FIG. 4 is a flow diagram of an overall method for employing an auto-tunecontroller to implement a tuning process that includes collectingmeasurements from a combustor and altering the fuel flow fractions basedon the measurements, in accordance with an embodiment of the presentinvention;

FIG. 5 is an exemplary graph of the application of stability bias overtime, according to an embodiment of the present invention;

FIG. 6 is a flow diagram of a method for automatically tuning acombustor of a gas turbine engine during transients, in accordance withan embodiment of the present invention; and

FIG. 7 is a flow diagram of a method for automatically tuning acombustor of a gas turbine engine during transients, in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION

The subject matter of the present invention is described withspecificity herein to meet statutory requirements. However, thedescription itself is not intended to limit the scope of this patent.Rather, the inventors have contemplated that the claimed subject mattermight also be embodied in other ways, to include different components,combinations of components, steps, or combinations of steps similar tothe ones described in this document, in conjunction with other presentor future technologies.

As one skilled in the art will appreciate, embodiments of the presentinvention may be embodied as, among other things: a method, system, orcomputer-program product. Accordingly, the embodiments may take the formof a hardware embodiment, a software embodiment, or an embodimentcombining software and hardware. In one embodiment, the presentinvention takes the form of a computer-program product that includescomputer-useable instructions embodied on one or more computer-readablemedia.

Computer-readable media include both volatile and nonvolatile media,removable and nonremovable media, and contemplates media readable by adatabase, a switch, and various other network devices. Network switches,routers, and related components are conventional in nature, as are meansof communicating with the same. By way of example, and not limitation,computer-readable media comprise computer-storage media andcommunications media.

Computer-storage media, or machine-readable media, include mediaimplemented in any method or technology for storing information.Examples of stored information include computer-useable instructions,data structures, program modules, and other data representations.Computer-storage media include, but are not limited to RAM, ROM, EEPROM,flash memory or other memory technology, CD-ROM, digital versatile discs(DVD), holographic media or other optical disc storage, magneticcassettes, magnetic tape, magnetic disk storage, and other magneticstorage devices. These memory components can store data momentarily,temporarily, or permanently.

Communications media typically store computer-useableinstructions—including data structures and program modules—in amodulated data signal. The term “modulated data signal” refers to apropagated signal that has one or more of its characteristics set orchanged to encode information in the signal. An exemplary modulated datasignal includes a carrier wave or other transport mechanism.Communications media include any information-delivery media. By way ofexample but not limitation, communications media include wired media,such as a wired network or direct-wired connection, and wireless mediasuch as acoustic, infrared, radio, microwave, spread-spectrum, and otherwireless media technologies. Combinations of the above are includedwithin the scope of computer-readable media.

As described above, embodiments of the present invention generallyrelate to automatically tuning a gas turbine engine. With reference toFIG. 1, a gas turbine engine 110 is depicted that accommodates aplurality of combustors 115. Generally, for the purpose of discussion,the gas turbine (GT) engine 110 may include any low emission combustors.In one instance, these low emission combustors may be arranged in acan-annular configuration about the GT engine 110. One type of GT engine(e.g., heavy duty GT engines) may be typically provided with, but notlimited to, 6 to 18 individual combustors, each of them fitted with acombustor liner, end cover, and casings. Another type of GT engine(e.g., light duty GT engines) may be provided with fewer combustors.Accordingly, based on the type of GT engine, there may be severaldifferent fuel circuits utilized for operating the GT engine 110.Further, there may be individual fuel circuits that correspond with eachof the plurality of combustors 115 attached to the GT engine 110. Assuch, it should be appreciated and understood that the auto-tunecontroller 150, and the tuning process executed thereby (see referencenumeral 400 of FIG. 4), can be applied to any number of configurationsof GT engines and that the type of GT engines describe hereinbelowshould not be construed as limiting on the scope of the presentinvention.

As discussed above, the plurality of combustors 115 (e.g., low emissioncombustors) may be prone to elevated levels of pressure fluctuationwithin the combustor liner. This pressure fluctuation is referred to as“combustion dynamics.” Left alone, combustion dynamics can have adramatic impact on the integrity and life of the plurality of combustors115, eventually leading to catastrophic failure. These combustiondynamics may be mitigated by adjusting fuel flow fractions of thecombustor gas flow between several groups of nozzles within theplurality of combustors 115. Generally, a fuel flow fraction is commonlyadjust for each of the plurality of combustors 115, thus the combustors(burners) are tuned alike, as opposed to tuning at the individual burnerlevel. These different “fuel flow fractions” are occasionally tuned toensure that acceptable levels (conventionally low levels) of thecombustion dynamics are maintained while, at the same time, promotingacceptable emission levels. The acceptable emission levels relate to theamount of pollutant that is generated by the GT engine 110. Schedules,which govern the fuel flow fraction for each fuel circuit, are typicallyhard coded into a control system (not shown) of GT engine 110. In oneinstance, these schedules are a function of a reference that could be,amongst other things, a turbine inlet reference temperature (TIRF) or aload on the GT engine 110.

Over time, several parameters will affect the combustion dynamics. Inparticular ambient condition changes and/or gas composition variationand/or normal wear may degrade the operation of the GT engine. Thisdegradation leads to regular “re-tuning” of the combustor to maintaincombustion dynamics and emissions within acceptable limits. As discussedherein, an automatic tuning control system, or the auto-tune controller150 of FIG. 1, is used to assess the state of the GT engine 110 and theplurality of combustors 115 in terms of parameters such as thecombustion dynamics, air flow, fuel flows, emissions, and pressuredistribution. Based on those parameters, the adequate fuel flowfractions are arrived upon by incrementally adjusting the fuel flowfractions until the alarm has been cleared, where the alarm is set upondetecting that an amplitude of a pressure pulse surpasses apredetermined upper limit. Accordingly, embodiments of the presentinvention concern the auto-tune controller 150 and the associated tuningprocess that enables automatic tuning of the combustion dynamics andemissions using small, consistent incremental changes of the fuel flowfraction.

An overall tuning process carried out by the auto-tune controller 150may comprise one or more of the steps described immediately below.Initially, various configurations of pressure signals of the pluralityof combustors 115 are monitored and recorded. These recorded pressuresignals are passed through a Fourier Transform, where the pressuresignals are converted into an amplitude versus frequency data format orspectrum. The amplitude and frequencies are then monitored and theamplitude is compared to a predetermined upper limit for eachpre-defined frequency band. The predetermined upper limit is generallydefined in terms of pounds per square inch (psi) for a predefinedfrequency bands. However, in other instances, the predetermined upperlimits may be expressed in other terms or units, where other types aredevices are used to measure performance of the combustors 115 (e.g.,accelerometers). If the determination is made that one or more of thefrequency-based amplitude exceeds its respective predetermined upperlimit for a pre-determined frequency band, then the auto-tune controller150 firstly determines which fuel flow fraction to adjust, and secondlyalters the fuel flow fraction associated with the specific frequencyband. This adjustment made to the fuel flow fraction is executed at apredefined amount.

Once the fuel flow fraction adjustment is made, the process reiterates.That is, the steps of monitoring and comparing the amplitude for anumber of predetermined frequency bands to a predetermined upper limit,and adjusting a predetermined fuel flow fractions are repeated if thedynamic pressure amplitude is above the predetermined upper limit.Specifically, when the dynamic pressure amplitude is ascertained toexist above the predetermined upper limit, the same predeterminedadjustment is made to the fuel flow fraction. The tuning process repeatsas required until the dynamic pressure amplitude falls below thepredetermined upper limit or until the fuel flow fraction cannot beadjusted any further.

If a first fuel flow fraction cannot be adjusted further, then either asecond fuel flow fraction is adjusted by a second predefined rate andthe tuning process repeats, or an alarm indication is issued to anoperator. With respect to adjusting the second fuel flow fraction, thetuning process repeats until the dynamic pressure amplitude falls underthe predetermined upper limit or the second fuel fraction cannot beadjusted any further. If a second fuel flow fraction cannot be adjustedfurther, then a third or more fuel flow fractions are adjusted.

Although a scheme for iteratively adjusting fuel flow fractions insuccession has been described immediately above, it should be understoodand appreciated by those of ordinary skill in the art that other typesof suitable schemes that adjust fuel flow fractions may be used, andthat embodiments of the present invention are not limited to thoseschemes that focus on one fuel flow fraction at a time. For instance,one embodiment of the tuning scheme may iteratively adjust a first fuelflow fraction by a predefined increment until the dynamic pressureamplitude falls under the predetermined upper limit or until aparticular number of iterations is reached, whichever occurs first. Ifthe particular number of iterations is reached, the tuning scheme causesa second fuel flow fraction to be iteratively adjusted by anotherpredefined increment until the dynamic pressure amplitude falls underthe predetermined upper limit or until another particular number ofiterations is reached, whichever occurs first. If the other particularnumber of iterations is reached, the tuning scheme returns to the firstfuel flow fraction. Specifically, the tuning scheme causes the firstfuel flow fraction to again be iteratively adjusted by the predefinedincrement until the dynamic pressure amplitude falls under thepredetermined upper limit or until a third particular number ofiterations is reached, whichever occurs first. The tuning scheme maythen return to the second fuel flow fraction or turn to a third fuelflow fraction for the purposes of adjustment.

With reference to FIGS. 1 and 4, an exemplary embodiment of the tuningprocess will now be described in detail. Initially, FIG. 1 illustratesan exemplary tuning environment 100 suitable for use in embodiments ofthe present invention. The exemplary tuning environment 100 includes theauto-tune controller 150, a computing device 140, and the GT engine 110.The auto-tune controller 100 includes a data store 135 and a processingunit 130 that supports the execution of the acquisition component 131,the processing component 132, and the adjustment component 133.Generally, the processing unit 130 is embodied as some form of acomputing unit (e.g., central processing unit, microprocessor, etc.) tosupport operations of the component(s) 131, 132, and 133 runningthereon. As utilized herein, the phrase “processing unit” generallyrefers to a dedicated computing device with processing power and storagememory, which supports operating software that underlies the executionof software, applications, and computer programs thereon. In oneinstance, the processing unit 130 is configured with tangible hardwareelements, or machines, that are integral, or operably coupled, to acomputer. In another instance, the processing unit may encompass aprocessor (not shown) coupled to the computer-readable medium (discussedabove). Generally, the computer-readable medium stores, at leasttemporarily, a plurality of computer software components that areexecutable by a processor. As utilized herein, the term “processor” isnot meant to be limiting and may encompass any elements of theprocessing unit that act in a computational capacity. In such capacity,the processor may be configured as a tangible article that processesinstructions. In an exemplary embodiment, processing may involvefetching, decoding/interpreting, executing, and writing backinstructions (e.g., reconstructing the physical gestures by presentinganimations of the motion patterns).

In addition, the auto-tune controller 100 is provided with the datastore 135. Generally, the data store 135 is configured to storeinformation associated with the tuning process or data generated uponmonitoring the GT engine 100. In various embodiments, such informationmay include, without limitation, measurement data (e.g., measurements121, 122, 123, and 124) provided by sensors 120 coupled to the GT engine110. In addition, the data store 135 may be configured to be searchablefor suitable access of stored information. For instance, the data store135 may be searchable for schedules in order to determine which fuelflow fraction to increment upon comparing measured dynamic pressureamplitude to a corresponding predetermined upper limit. It will beunderstood and appreciated that the information stored in the data store135 may be configurable and may include any information relevant to thetuning process. The content and volume of such information are notintended to limit the scope of embodiments of the present invention inany way.

In embodiments, the auto-tune controller 100 will record look-up tables(e.g., utilizing the data store 135 of FIG. 1). These look-up tables mayinclude various information related to the operational conditions of theGT engine and combustors attached thereto. By way of example, thelook-up tables may include an operating curve with a suggested toleranceband that defines the outer limits of efficient operation. Uponperforming the process of automatically tuning the GT engine, theauto-tune controller may be automatically reprogrammed to record aspectsof the tuning process in the operating curve. That is, the operatingcurve in the look-up table is altered to reflect occurrences during, andresults from, the tuning process. Advantageously, the altered operatingcurve may be access during the next tuning procedure, thus, making eachsubsequent tuning more efficient (e.g., reduce the number of fuel flowadjustment increments needed to bring a condition below the predetermineupper limit). In this way the look-up table (e.g., operational matrix)can be automatically developed through the incremental adjustment of oneparameter at a time. Since the incremental adjustment is stored in theoperational curve, the auto-tune controller learns the optimum tuningperformance for any particular operating system. This greatly reducesthe amount of tuning required which will be beneficial for units on autogrid control (AGC) where stable points may be infrequent or for unitsexperiencing sudden cyclic variations in fuel properties or ambientconditions.

In some embodiments, should the tuning by way of adjusting the fuel flowfraction not alleviate an emissions or dynamics alarm, an incrementalbias can be supplied to adjust fuel temperature from the optimumout-of-compliance fraction tuning point identified per the sectionabove. However, if incrementally biasing the fuel temperature is not anoption—due to absent or limited fuel temperature manipulationability—and the unit remains in alarm mode, a request may be issued toallow adjustment of the firing curve of the GT device. If the operatorrequest is granted, an incremental firing temperature bias is providedto the existing unit firing curve at the optimum out-of-compliance pointdescribed in the above section.

With continued reference to the look-up table stored on the auto-tunecontroller 100, variations of the look-up table configuration will nowbe described. In one instance, a number of look-up tables are providedthat graph fractions versus TIRF, or load. Each of these look-up tablesrelate to a combination of a number of ambient temperatures and gasparameters. The “gas parameter” is characteristic of the gas compositionand properties, and may be implemented as a relative value as comparedto a nominal initial value. The tuning adjustment is performed at astable TIRF, or load. Whenever an incremental bias adjustment is neededbecause an alarm level or emission level was exceeded, the algorithmfirst determines which ambient temperature and gas parameter family theunit is operating in, and then which fuel fraction to change and inwhich direction. Secondly, the desired bias increment (upwards ordownwards) and the current TIRF, or load, is recorded. The algorithmthen determines which table shall be modified depending on the recordedambient temperature and gas parameter. Once defined, the algorithmdetermines which points in the fraction versus TIRF graph are bracketingthe current value for TIRF. Upon identifying those two points, the biasvalue for the two points is incrementally modified (upwards ordownwards), and the increment is stored in the correct look-up table.

Further, the exemplary tuning environment 100 includes the computingdevice 140, which is operably coupled to a presentation device 145 fordisplaying a user interface (UI) display 155 that warns an operator of afailure to automatically tune the GT engine 100. The computing device140, shown in FIG. 1, may take the form of various types of computingdevices. By way of example only and not limitation, the computing device145 may be a personal computer, desktop computer, laptop computer,handheld device, consumer electronic device (e.g., pager), handhelddevice (e.g., personal digital assistant), various servers, and thelike. It should be noted, however, that the invention is not limited toimplementation on such computing devices, but may be implemented on anyof a variety of different types of computing devices within the scope ofembodiments of the present invention.

With reference to FIG. 4, a tuning process 200 will now be discussed inlight of the exemplary tuning environment 100 of FIG. 1. Generally, FIG.4 is a flow diagram of an overall method 400 for employing the auto-tunecontroller 150 of FIG. 1 to implement a tuning process that includescollecting measurements from the plurality of combustors 115 andaltering the fuel flow fractions based on the measurements, inaccordance with an embodiment of the present invention. Initially, theoverall method 400 includes monitoring data that represents combustiondynamics of the GT engine 100. In one embodiment, the combustiondynamics 122 are measured for each of the plurality of combustors 115using the sensors 120 (e.g., pressure transducers) that communicate themeasurement data to the acquisition component 131. In anotherembodiment, the sensors 120 communicate emissions 121 that are detectedfrom the GT engine 100. In yet other embodiments, the measurement datacollected from the GT engine 110 may include, but is not limited to, GTparameters 123 and gas manifold pressures 124.

In some instances, the data collected from the GT engine 100 isnormalized. For instance, the sensors 120 may be configured as pressuretransducers that detect pressure fluctuations in each of the pluralityof combustors 115 and report those fluctuations as the combustiondynamics 122. The fluctuations may be measured over a time period andsent to the acquisition component 131 in the form of a rolling averageof pressure variability.

Step 430 of the overall method 430 pertains to passing the measured datathrough a Fourier Transform, or another appropriate algorithm, in orderto convert the data to an amplitude versus frequency format (utilizingthe processing component 132 of FIG. 1). This amplitude versus frequencyformat may take on a variety of configurations, such as a graph, achart, or a matrix, and is referred to hereinbelow as a “spectrum.” Inone instance, when the amplitude versus frequency format takes on theconfiguration of a matrix, the matrix may include the followingcategories of values: combustor identity, frequency, and amplitude.

In embodiments, the spectrum may be divided by frequency range, ordiscretized, into a number of frequency bands, where each band has itsown predetermined upper limit in terms of amplitude. The spectrum may bediscretized into any number of frequency bands. In one instance, thespectrum is discretized into 4-6 frequency bands, or windows, based onthe type of GT engine 100 being tuned, where each frequency bandexpresses a different parameter. In operation, when the predeterminedupper limit (i.e., alarm level limit) for a particular frequency band isexceeded, the schedule instructions the auto-tune controller 150 whichfuel flow fraction to change and in which direction (upwards ordownwards) to make an adjustment. Typically, the proper fuel flowfraction to change and the proper manner of adjustment are selectedbased on the type of measured data being processed (e.g., combustordynamics or emission levels) and the nature of the measured data beingprocessed (e.g. combustor dynamics tone, type of emission such as NOx orCo).

In step 440, a maximum dynamic pressure amplitude is identified withineach of the frequency bands. This maximum dynamic pressure amplitude maybe determined by selecting the maximum dynamic pressure amplitude foreach class of measured data (combustion dynamics 122) within one or moreof the frequency bands. Both the predetermined upper limit (i.e., alarmlimit level) and the maximum dynamic pressure amplitude derived fromeach frequency band are measured in terms of pounds per square inch(psi).

As depicted in step 450, the identified maximum dynamic pressureamplitude is compared against an appropriate predetermined upper limit.(There is no specific priority order to comparing or addressing outliermaximum frequencies.) This predetermined upper limit may be based on atype of measured data being evaluated and/or the fuel circuit beingtuned. Upon comparison, a determination of whether the maximum dynamicpressure amplitude exceeds the predetermined upper limit is performed,as depicted at step 460. If the maximum dynamic pressure amplitude doesnot exceed the predetermined upper limit, such that the GT engine 100 isoperating within a suggested range with respect to the particularmeasured data, the tuning process moves to another condition. That is,the tuning process proceeds to monitor and evaluate another set ofmeasured data, as depicted at step 470. By way of clarification, justthe dynamic pressure amplitude is monitored in a series of frequencybins. Other parameters are not a function of frequency bins, but stillare subject to maximum tuning limits.

If, however, the maximum dynamic pressure amplitude does exceed thepredetermined upper limit, a fuel flow fraction is selected foradjustment. This is indicated at step 480 of FIG. 4. As discussed above,the appropriate fuel flow fraction is selected by a schedule, asdiscussed more fully below with reference to FIGS. 2 and 3. Thisselected fuel flow fraction is then incrementally adjusted by apre-specified amount, as depicted at step 490. Incrementally adjustingthe fuel flow fraction may be accomplished by the adjustment component133 of FIG. 1 transmitting an incremental bias adjustment 160 to atleast one of the plurality of combustors 115 mounted to the GT engine100. In one embodiment, automatic valves on the combustors 115 adjustthe fuel flow fraction for a subject fuel circuit in response torecognizing the incoming incremental bias adjustment 160.

This predefined amount is typically based on testing experience and thecombustor identity (as provided by the matrix). In one instance, thepredefined amount of incremental adjustment is 0.25% adjustment of thefuel flow fraction between the injection ports. Accordingly, byincrementing a fuel flow fraction upwards or downwards by thepre-specified amount, the pattern of fuel flow distribution throughinjection points is altered. However, even though the fuel flow fractionis changed, the total fuel flow to the fuel circuit is generally heldconstant.

Upon applying the incremental bias adjustment 160, the auto-tunecontroller 150 waits a period of time before acquiring and processingdata extracted from the GT engine 100. This is depicted at step 500 ofFIG. 4. Waiting the period of time ensures that the GT engine 100stabilizes before checking to determine whether adjusting the fuel flowfraction was sufficient to tune the GT engine 100. In embodiments, theperiod of time that is waited between adjustments may vary based on thetype of parameter, or measured data, being processed. For instance, theperiod of time required to stabilize a combustion dynamic may be lessthat the period of time required to stabilize emissions.

At step 510, a determination is performed to ascertain whether a maximumnumber of increments has been reached. If the maximum number ofincrements that the fuel flow fraction can be adjusted is not reached,the process is allowed to reiterate. Accordingly, the fuel flow fractioncan be adjusted at least one more time if the comparison step 450indicates that further incremental adjustment is needed. However, if themaximum number of increments that the fuel flow fraction can be adjustedis not reached, then either another fuel flow fraction can be adjusted(as determined by the schedule), or an alert is sent to an operator.This is depicted at step 520. In one embodiment, an alarm indicator 180is sent to the computing device 140 by the processing component 132. Inresponse to the alert, the operator may take action to manually tune theGT engine 100 or contact a technician to service the GT engine 100.

In some embodiments, sending an alert to the operator is the firstaction that is taken, as instructed by the schedule. That is, if themeasured data for a particular parameter, upon processing the datathrough the Fourier Transform, exceeds a corresponding predeterminedupper limit, then the first action taken is notifying the operator ofthe discrepancy, as opposed to incrementally adjusting a fuel flowfraction.

Another embodiment allows the operator to allow the auto-tune controller150 to incrementally adjust the fuel gas temperature and/or the firingtemperature to achieve in compliance operation.

Turning now to FIG. 2, an exemplary chart 200, or schedule, depictingrecommended fuel flow fraction adjustments for a fuel-rich condition areprovided, in accordance with an embodiment of the present invention. Asillustrated, the chart 200 includes an indication 210 of the type offuel being consumed by the GT engine being tuned. Further, the chartincludes a row 220 that lists the conditions being monitored. In thisexemplary chart 200, there are four conditions being monitor, which areparameters A-D. Although four conditions are monitored in this instance,the number of monitored conditions should not be construed as limiting,as any number of conditions may be observed for auto-tuning the GTengine. Generally, parameters A-D may represent particular conditionsthat are measured using pressure transducers, emissions-testing devices,accelerometers, and other items that are capable of monitoring theoperation of the GT engine. By way of example, parameter A may representLean-Blowout (LBO), parameter B 221 may represent Cold Tone (CT),parameter C may represent Hot Tone (HT), and parameter D may representNitrogen-Oxides (NOx). Accordingly, in this example, parameters A-Crelate to pressure data, while parameter D relates to a gas composition.Typically, the gas composition is determined by monitoring theconcentrations levels of emissions (e.g., CO and NOx). A tuning processwith incremental adjustments, similar to the one described above, may beused in connection with conditions that involve emissions.

Each of parameters A-D is automatically monitored during the tuningprocess. Further, the data monitored during the tuning process isprocessed via the Fourier Transform to determine a maximum amplitude foreach condition. If any of the maximum amplitudes for these conditionsexceeds or falls below an individual, predetermined limit mapped to eachof the parameters A-D, respectively, the actions 230 are carried out.

By way of example, if the maximum amplitude for parameter B 221 (e.g.,the CT condition) exceeds an individual, predetermined upper limitmapped to parameter B 221, the actions 231, 232, and 233 are carried outbased on the ordering 250. Specifically, if the maximum dynamic pressureamplitude for the parameter B 221 exceeds the predetermined upper limit,the FRACTION 2 232 is initially increased by the incremental amount, asindicated by the ordering 250. Then, upon recursively increasing theFRACTION 2 232 by an incremental amount until the maximum number ofadjustments for that fuel flow fraction is reached, the FRACTION 1 231is decreased. Next, if adjusting the FRACTION 1 231 is ineffective, theFRACTION 3 233 is exercised. Last, if adjusting the FRACTION 3 233 isineffective to reduce the maximum frequency amplitude below thepredetermined upper limit, an alarm is sent to an operator. As will berecognized in the relevant field, the exemplary method above is just anexample of a process for auto-tuning a particular engine, such as the7FA Engine, and there will be different methods, which include differentmonitored parameters and varied fuel flow fractions, for auto-tuningother engines.

Although a single configuration of a schedule (e.g., chart 200) forselecting which actions to take in light of the predetermined upperlimits being exceeded has been described, it should be understood andappreciated by those of ordinary skill in the art that other types ofsuitable schedule that provide an organized hierarchy of actions may beused, and that embodiments of the present invention are not limited tothe conditions and actions of the schedule described herein. Inaddition, it should be noted that the auto-tune controller can be usedwith a variety of combustion systems. Therefore, the present inventionis not limited to just three fuel fraction adjustments. The exactquantity of fuel nozzles and fuel flow fractions can vary depending onthe combustor configuration and type of GT engine being tuned. So, for adifferent combustion system, the number of adjustment points could begreater or fewer than those depicted in the present disclosure withoutdeparting from the essence of the present invention.

Further, the chart 200 depicts adjustments to fuel flow fractions inresponse to multiple frequency bands for various monitored conditions.In the event that multiple frequencies exceed their respectivepredetermined upper limits, no preference or priority is made by theauto-tune controller for determining which frequency to address first.However, in other instances, some preferential guidelines are utilizedby the auto-tune controller 150 of FIG. 1 to make decisions as to whichorder the frequencies are addressed.

With reference to FIG. 3, an exemplary chart 300 depicting recommendedfuel flow fraction adjustments 320 for a combustor that is provided withtwo injection ports is shown, in accordance with an embodiment of thepresent invention. Because, only two injection ports are provided, thereis only one fuel flow fraction that can be adjusted to distribute fuelbetween the injection ports provided. Further, two conditions 310 of theGT engine being tuned are measured in this instance. These conditions310 are represented by Parameter A and Parameter B. If either ParameterA or B exceeds a corresponding, predetermined upper limit, the scheduleindicates which of the fuel flow fraction adjustments 320 to take. Ifadjusting the prescribed fuel flow fraction a maximum recommended numberof times does not bring the GT engine into a normal operational range,then the next step involves sending an alarm to an operator orautomatically placing a call to a technician.

Various benefits arising from automatic tuning can be realized whenautomatic tuning is compared against the current tuning processes. Thatis, because the tuning process of the present invention can beimplemented automatically, the disadvantages of manually tuning areovercome. For instance, automatically tuning can be performed quicklyand often, which will substantially prevent degradation that would haveoccurred before the manual tuning. Further, frequently tuning reducesexcess pollutants/promotes lower emissions while improving engine life.

Embodiments of the present invention have been described in relation toauto-tuning a combustor of a gas turbine engine during normal operationof the combustor. In other embodiments, auto-tuning may be performedduring a transient period of operation or during a specific change ofstate (e.g., activation of water wash system or inlet bleed heat valvemodulation). As used herein, a transient period, also referred to as atransient, is when the load of the gas turbine engine is changing, suchas being increased or decreased. More specifically, a transient mayrefer to a rapid increase or a rapid decrease in load of the gas turbineengine. Tuning during a transient period is typically not performed,which can lead to issues such as a flameout, also termed a lean blowout(LBO). An LBO can occur when the local fuel to air ratio (FAR) in thereaction zone falls below the lean flammability limit. In such case theflame is too lean to maintain stability and begins to fluctuate andcreating low frequency acoustic pulsations called LBO tones. Eventuallyif such lean instability continues, the flame in one or more of thecombustion chambers may get extinguished and the turbine will forcefullyshutdown. However, utilizing embodiments of the present invention,tuning is performed during a transient period, such as when the load isbeing increased or decreased or during a specific change of state tomaintain flame stability and avoid LBO.

Tuning during a transient period or a specific change of state isaccomplished by applying a stability bias to the tuning system. A changeof the state of the gas turbine engine is indicated by a valve position,water injection flow rate, or exhaust temperature variations. Asreferred to herein, a stability bias is a process that incrementallyadjusts a fuel flow fraction to locally enrich the reaction zone in thecombustor thus locally increasing the flame temperature to maintain astable flame. In one embodiment, the stability bias is applied to theoperation of the gas turbine engine when at least two conditions aremet. For instance, in this embodiment, if a transient occurs (e.g.,rapid increase or decrease in load) and it is determined that a LBO isimminent, the stability bias may be applied. Determining that an LBO isimminent may be based on monitoring of parameters or conditions of thegas turbine engine. One or more of many parameters and conditions may bemonitored, including, for exemplary purposes only, a lean blowoutdynamics amplitude, the ratio of lean blowout dynamics amplitude to hottones dynamics amplitude (LBO/HT), cold tones dynamics amplitudes, andthe like. Other parameters and conditions not specifically mentionedherein may also be monitored to detect early indicators of LBO.

As mentioned, the stability bias is applied to the system until thesystem is operating in a steady state or as long as the LBO conditionsare present. In one embodiment, when the system is running in a steadystate, the conditions being monitored indicate that a lean blowout is nolonger imminent. For instance, if LBO/HT is being monitored and haspreviously indicated an imminent LBO, when LBO/HT no longer indicates animminent LBO, the application of the stability bias may be terminated.In one embodiment, the stability bias is applied and/or graduallyterminated. The application and removal of the stability bias isillustrated and described in more detail in relation to FIG. 5 herein.In general, the rate of application will be as fast as the controllerallows, and will be removed gradually to prevent destabilizing thecombustor.

FIG. 5 illustrates an exemplary graph 500 of the application ofstability bias over time, according to an embodiment of the presentinvention. Here, the vertical axis of graph 500 represents the amplitudeof the stability bias applied, while the horizontal axis representstime. Among other things, graph 500 illustrates the application andtermination of the stability bias based on presence or absence of LBOindicators. At item 502, it is shown that no stability bias based onpresence or absence of LBO indicators or that a specific change of stateis detected. At item 504, an unstable load is detected, meaning that itis detected that the load in the gas turbine engine is increasing ordecreasing. In one embodiment, the load is rapidly increasing or rapidlydecreasing. Also at item 504, LBO indicators were detected. As shown,the stability bias is applied, and may be immediately applied inembodiments. The stability bias is ramped up at a particular rate. Therate at which the stability bias is ramped up may be dependent upon, inone embodiment, the particular controller being utilized for the gasturbine engine. In an alternative embodiment, the ramp-up rate of theapplication of the stability bias may depend upon how imminent the leanblowout is, or the values of the conditions being monitored in the gasturbine engine. For instance, if it is determined that the possibilityof a lean blowout occurring is less imminent, the stability bias may beapplied at a slower rate than if it is determined that the possibilityof a lean blowout occurring is more imminent, in which case thestability bias may be applied at a faster rate.

Once the stability bias has been ramped up, the full stability bias isapplied, shown as item 506. While the stability bias is applied, one ormore conditions associated with the operation of the gas turbine engineare monitored, such as on a continuous basis. For example, lean blowout,hot tone, cold tone, NOx, and other parameters and conditions may bemonitored while the stability bias is applied to determine that a fuelflow fraction is to be adjusted, and to even determine which fuel flowfraction to adjust. Details regarding auto tuning of the gas turbineengine are provided above in relation to auto tuning during normaloperation. While embodiments described in relation to FIG. 5 relate toauto tuning of the gas turbine engine during transient, previousdiscussions herein regarding incremental tuning apply here as well. Thefull stability bias is applied, in one embodiment, until the monitoredLBO indicators are no longer present. Alternatively or in addition tothis, the stability bias may be applied until steady state conditionsare reached, also indicating that lean blowout is no longer imminent.

As shown at item 508, LBO indicators subside/recede and imminent LBO isno longer detected. At this time, ramp down of the stability bias isapplied. Here, the stability bias is gradually decreased to ensuresmooth transition. Once ramp down of the stability bias is completed,the stability bias is no longer applied to the gas turbine engine, shownat item 510.

FIG. 6 illustrates a method 600 for automatically tuning a combustor ofa gas turbine engine during transients, in accordance with an embodimentof the present invention. At step 602, it is determined whether a stateof the change of the gas turbine engine is changing. In one embodiment,this may be determined based on a valve position, water injection flowrate, or exhaust temperature variations. In one embodiment, a statechange is a change in load, for instance, a rapidly increasing orrapidly decreasing load. Or, a state change may refer to activation ofwater wash system or inlet bleed heat valve modulation. Other examplesof state changes not specifically mentioned herein are also contemplatedto be within the scope of the present invention. At step 604, conditionsof the gas turbine engine are monitored to determine whether a leanblowout is imminent or that a specific change of state has occurred. Theconditions monitored may include, for example, a lean blowout dynamicsamplitude, a ratio of a lean blowout dynamics amplitude to hot tonesdynamics amplitude, or a cold tones dynamics amplitude. Other conditionsnot specifically mentioned herein may be monitored as early indicatorsof LBO.

At step 606, a stability bias is applied to the gas turbine engine. Forinstance, the stability bias may be applied upon determining that eitheror both of the lean blowout is imminent or that a specific change ofstate has occurred. In one embodiment, the stability bias comprisesmonitoring operating conditions of the gas turbine engine, determiningwhether the operating conditions have overcome a threshold value, andwhen the threshold value is overcome, adjusting a fuel flow fraction bya predefined increment. Adjusting a fuel flow fraction may compriseapplying a uniform amount of adjustment to the fuel flow fraction orapplying a varying amount of adjustment to the fuel flow fraction.Varying the amount of adjustment to the fuel flow fraction may be basedupon a number of predefined adjustments previously made to the fuel flowfraction or an identity of the fuel flow fraction presently beingadjusted. The operating conditions being monitored during application ofthe stability bias may include emissions of the gas turbine engine,including NOx, CO, etc. In another embodiment, the operating conditionscomprise combustor dynamics that include lean blowout, cold tone, hottone, and screech. In one embodiment, adjusting the fuel flow fractionby the predefined increment may include making a determination toincrease or decrease the fuel flow fraction as a function of theoperating conditions that overcome the threshold value. In anotherembodiment, adjusting the fuel flow fraction comprises making adetermination to increase or decrease the fuel flow fraction as afunction of a type of the fuel flow fraction selected for adjustment.The stability bias is immediately applied in one embodiment.

At step 608, it is determined that lean blowout is no longer imminent.Upon determining that the lean blowout is no longer imminent or that thesystem has reached steady state (e.g., no rapid increase or decrease inload), the application of the stability bias is gradually terminated,shown at step 610.

Turning now to FIG. 7, a flow diagram is illustrated for an alternativemethod 700 for auto-tuning a gas turbine engine during transients. Atstep 704, conditions of the gas turbine engine are monitored todetermine that one or both of a lean blowout is imminent or that a stateof the gas turbine engine is changing. A stability bias is applied tothe gas turbine engine at step 706. In one embodiment, the stabilitybias is applied while the lean blowout is imminent. The stability biascomprises monitoring operating conditions of the gas turbine engine,determining whether the operating conditions have overcome a thresholdvalue, and when the threshold value is overcome, adjusting a fuel flowfraction by a predefined increment. The fuel flow fraction may govern aportion of a total fuel flow that is directed to each fuel nozzle of thecombustor's fuel circuit. At step 708, when the lean blowout is nolonger imminent, the application of the stability bias is graduallyterminated.

The present invention has been described in relation to particularembodiments, which are intended in all respects to be illustrativerather than restrictive. Alternative embodiments will become apparent tothose of ordinary skill in the art to which the present inventionpertains without departing from its scope.

From the foregoing, it will be seen that this invention is one welladapted to attain all the ends and objects set forth above, togetherwith other advantages which are obvious and inherent to the system andmethod. It will be understood that certain features and sub-combinationsare of utility and may be employed without reference to other featuresand sub-combinations. This is contemplated by and within the scope ofthe claims.

What is claimed is:
 1. A method of operating a system for automaticallystabilizing combustor dynamics or emissions of a gas turbine engine byemploying a tuning process during transients, the method of operatingthe system comprising: providing a gas turbine engine including one ormore combustors that are each provided with a fuel flow fraction forgoverning a portion of a total fuel flow that is directed to each fuelnozzle of the combustor's fuel circuit; and carrying out a tuningprocess comprising: (a) determining, with an auto-tune controller, thata load of the gas turbine engine is changing from a steady state to anunsteady state, (b) determining, with the auto-tune controller, that alean blowout parameter overcomes a predetermined threshold value, and(c) applying, using the auto-tune controller, a stability bias to thegas turbine engine in response to determining that the lean blowoutparameter overcomes the predetermined threshold value, the stabilitybias comprising adjusting the fuel flow fraction based on the leanblowout parameter overcoming the predetermined threshold value.
 2. Themethod of claim 1, wherein the lean blowout parameter includes one ormore of a lean blowout dynamics amplitude, a ratio of a lean blowoutdynamics amplitude to a hot tones dynamics amplitude, or a cold tonesdynamics amplitude.
 3. The method of claim 1, further comprising:accessing a schedule to select an appropriate fuel flow fraction toalter; and selecting a first fuel flow fraction to alter upon inspectingthe schedule.
 4. The method of claim 3, wherein the tuning processfurther comprises: utilizing the schedule to determine an incrementalamount to adjust the first fuel flow fraction; and utilizing theschedule to determine a direction in which to make the adjustment to thefirst fuel flow fraction.
 5. The method of claim 4, wherein the tuningprocess further comprises: upon making the adjustment to the first fuelflow fraction, determining a number of adjustments recursively made tofirst fuel flow fraction; and when the number of recursive adjustmentsreaches an allowable number of iterations, taking an action prescribedby the schedule.
 6. The method of claim 5, wherein the action prescribedby the schedule includes at least one of adjusting a second fuel flowfraction, alerting an operator, adjusting a fuel gas temperature, oradjusting a firing temperature.